2023-02-03 13:23:02

by Anton Gusev

Subject: [PATCH] efi: fix potential NULL deref in efi_mem_reserve_persistent

When iterating on a linked list, a result of memremap is dereferenced
without checking it for NULL.

This patch adds a check that falls back on allocating a new page in
case memremap doesn't succeed.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 18df7577adae ("efi/memreserve: deal with memreserve entries in unmapped memory")
Signed-off-by: Anton Gusev <[email protected]>
---
drivers/firmware/efi/efi.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index a2b0cbc8741c..48d30c806d94 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -1007,6 +1007,8 @@ int __ref efi_mem_reserve_persistent(phys_addr_t addr, u64 size)
/* first try to find a slot in an existing linked list entry */
for (prsv = efi_memreserve_root->next; prsv; ) {
rsv = memremap(prsv, sizeof(*rsv), MEMREMAP_WB);
+ if (!rsv)
+ break;
index = atomic_fetch_add_unless(&rsv->count, 1, rsv->size);
if (index < rsv->size) {
rsv->entry[index].base = addr;
--
2.39.1

2023-02-03 13:29:34

by Ard Biesheuvel

Subject: Re: [PATCH] efi: fix potential NULL deref in efi_mem_reserve_persistent

On Fri, 3 Feb 2023 at 14:23, Anton Gusev <[email protected]> wrote:
>
> When iterating on a linked list, a result of memremap is dereferenced
> without checking it for NULL.
>
> This patch adds a check that falls back on allocating a new page in
> case memremap doesn't succeed.
>
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>
> Fixes: 18df7577adae ("efi/memreserve: deal with memreserve entries in unmapped memory")
> Signed-off-by: Anton Gusev <[email protected]>
> ---
> drivers/firmware/efi/efi.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index a2b0cbc8741c..48d30c806d94 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -1007,6 +1007,8 @@ int __ref efi_mem_reserve_persistent(phys_addr_t addr, u64 size)
> /* first try to find a slot in an existing linked list entry */
> for (prsv = efi_memreserve_root->next; prsv; ) {
> rsv = memremap(prsv, sizeof(*rsv), MEMREMAP_WB);
> + if (!rsv)
> + break;

Thanks for the patch.

Why do you think 'break' is the correct action here?


> index = atomic_fetch_add_unless(&rsv->count, 1, rsv->size);
> if (index < rsv->size) {
> rsv->entry[index].base = addr;
> --
> 2.39.1
>